1. Field of Invention
The present invention relates to a very large area display for use in outdoor and stadium environment employing plasma display technology. More particularly, the present invention utilizes sub-blocks of tiles of plasma pixels that are specially designed to have high luminous efficiency.
2. Description of Prior Art
For large area, size of several feet in diagonal, display applications such as stadium display system, bill board display system and other outdoor and indoor display systems, several display technologies have been described. For example, Cathode Ray Tubes (CRTs), Fluorescent Lamps (FLs), Plasma Display Panels (PDPs) and fiber bundles carrying the light have been described in the prior art for these applications. These applications demand high performance of displays in terms of (i) brightness for readability under sunlight (ii) luminous efficiency (iii) planarity (iv) weight (v) ease of manufacturing (vi) Operation under temperature and humidity extremes.
In one prior art (U.S. Pat. No. 4,529,909), Kamegaya et.al described a gas discharge display panel that employed discrete anodes and cathodes arranged between two substrates orthogonally. The cathodes were hollow cathodes. For a very large screen display of several feet in diagonal, it is extremely difficult to deal with substrates of several feet and carry out processes on them in manufacturing. In another prior art (U.S. Pat. No. 4,833,542), Hara et.al described a large area display using CRTs as light emitting elements. As is well known, CRTs are bulky and heavy for such applications. Lowry et.al (U.S. Pat. No. 6,396,985) used fiber-optic bundles to transmit images from one end of the fiber bundle to the other end that was spread and terminated in a surface forming a tile-like structure. Lowry et.al employed optical lenses and refractive micro-lenses to preserve the image with minimum distortion. The image is generated at the dense end of the fiber bundle. This invention was mainly on optical communication of images in a large screen and by itself did not create display images. This was a bulky system with two sections comprising image generation and image communication and hence was bulky and complex in optical assembly. In another prior art (U.S. Pat. No. 5,095,244) Maeda et.al used fluorescent display tube as the main display screen. The fluorescent display tube was vacuum based flat CRT that employed control grid and focus electrodes to control the electron beam that impinged on Red, Blue and Green phosphors. This type of flat CRT is not suitable for several feet diagonal display and is heavy and bulky. Another prior art (U.S. Pat. No. 6,452,326 and US Patent Application No. 20040130252) by Xiaoqin Ge et.al employed discrete cold cathode fluorescent lamps (CCFLs) as picture elements (pixels). The display screen consisted of CCFLs of red color, blue color and green color assembled close to each other to form a color pixel. The CCFLs with several bends were assembled inside a flat vessel to be contained in a pixel format. The fill factor of each color was different inside the pixel. The CCFLs were scanned by incoming data to generate images. The disadvantage with this technique is the bulkiness and discrete nature associated with the whole display screen. In a publication (Tsutae Shinoda, Manabu Ishimoto, Hitoshi Yamada, Akira Tokai and Kenji Awamoto—“New approach for wall display with fine plasma tube array technology”—SID 02 Digest of Technical papers, pp. 1072-1075, SID 2002 International Symposium vol. XXXIII, No. 2, May 2002), Tsutae et.al described a large stack of linear plasma tubes as light generating pixel elements for very large area out door and indoor stadium type application. Electrodes were placed external to the plasma tubes and plasma was confined through the positioning of electrodes. In this configuration plasma diffused out of the confined region and further discrete tubes were bulky.
Another prior art (U.S. Pat. No. 5,668,443) by Kawaguchi et.al used discrete fluorescent lamps with coaxial geometry of electrodes. The tubes were assembled with ends-on with the light coming through a cylindrical tunnel. Most of the light loss occurred through multiple reflections as the light came from the inner surface of the coaxial cylinder to the end of the tube that formed the pixel. Several tubes were stacked end-on to form a pixel. This configuration was bulky and less efficient due to light loss. In a publication (Large area color display “Skypix”—Yoshiyasu Sakagauchi et.al, SID' 92 Digest of Technical papers, SID International Symposium, May 1991), Yoshiyasu Sakaguchi et.al described another cylindrical fluorescent lamp with hot cathode. In this configuration with end-on side acting as pixel, lot of light loss occurs with system being bulky due to the depth of cylindrical fluorescent lamps.
In all the foregoing arts, the thickness of the display was high and the display was bulky with discrete components. In some of them, the tiled concept was only at the final surface with increased thickness and bulkiness behind the tiles.